This invention relates to a process for recovering lube oil base stocks from used motor oil formulations. In particular, this invention relates to the removal of metallic additive packages from the waste oil to facilitate further processing of the used motor oil. The invention further relates to asphalt blend compositions containing used motor oil bottoms from the process, and asphalt pavement compositions containing the asphalt blend compositions.
Automotive lubricating oils are usually formulated from paraffin based petroleum distillate oils or from synthetic base lubricating oils. Lubricating is oils are combined with additives such as soaps, extreme pressure (E.P.) agents, viscosity index (V.I.) improvers, antifoamants, rust inhibitors, antiwear agents, antioxidants, and polymeric dispersants to produce an engine lubricating oil of SAE 5 to SAE 60 viscosity.
After use, this oil is collected from truck and bus fleets, automobile service stations, and municipal recycling centers for reclaiming. This collected oil contains organo-metallic additives such as zinc dialkylthiophosphate from the original lubricating oil formulation, sludge formed in the engine, and water. The used oil may also contain contaminants such as waste grease, brake fluid, transmission oil, transformer oil, railroad lubricant, crude oil, antifreeze, dry cleaning fluid, degreasing solvents such as trichloroethylene, edible fats and oils, mineral acids, soot, earth and waste of unknown origin.
Reclaiming of waste oil is largely carried out by small processors using various processes tailored to the available waste oil, product demands, and local environmental considerations. Such processes at a minimum include chemical demetallizing or distillation. The presence of organo-metallics in waste oils such as zinc dialkylthiophosphate results in waste oils becoming sticky, overly viscous and thus difficult if not impossible to process. Moreover, the resulting sludge created reduces the amount of salable product, as well as creating additional disposal problems.
Successful reclaiming processes require the reduction of the organo-metallics (or ash) content to a level at which the hot oil does not become sticky. Such reduction can be carried out by chemical processes which include reacting cation phosphate or cation sulfate with the chemically bonded metal to form metallic phosphate or metallic sulfate. U.S. Pat. No. 4,432,865 to Norman, the contents of which are incorporated herein by reference, discloses contacting used motor oil with polyfunctional mineral acid and polyhydroxy compound to react with undesired contaminants to form easily removable reaction products. These chemical processes suffer from attendant disposal problems depending on the metal by-products formed. Ash content can also be reduced by heating the used lubricating oil to decompose the organo-metallic additives. However, indirect heat exchange surfaces cannot be maintained above 400xc2x0 F. (204xc2x0 C.) for extended periods without extensive fouling and deposition of metals from the additives. Used lubricating oils can be heated to an additive decomposition temperature of 400xc2x0 F. (204xc2x0 C.) to 1000xc2x0 F. (538xc2x0 C.) by direct heat exchange by mixing with a heated product oil as disclosed in U.S. Pat. No. 5,447,628 to Harrison, et al., the contents of which are incorporated herein by reference. Although ""628 claims to be direct contact heat exchange, the xe2x80x9ccontactxe2x80x9d occurs when the UMO is added to lower portion of a fractionator having a fired heater. U.S. Pat. No. 4,101,414 to Kim, et al., incorporated herein by reference, discloses predistillation by steam stripping for several hours of a used lubricating oil stock in order to remove light oil, residual water, sulfur, and NOx. The temperature is kept at temperatures which avoid additive breakdown, and the process provides a concentrate product upon vacuum distillation. Flow processes using heat exchange by direct contact with hot hydrogen have been proposed but are expensive in view of the costs associated with hydrogen compression and hydrogen""s low heat capacity. Such processes include UOP""s Hy-Lube described in U.S. Pat. Nos. 5,244,565 and 5,302,282 which feature an initial used oil feed fractionation step to remove sludge and a majority of metals utilizing a hot circulating hydrogen stream as a heating medium to avoid deposition of decomposed organo-metallic compounds on heating surfaces, followed by a hydrotreating circuit with caustic neutralization to eliminate chlorides, with a final product fractionation step. Flow processes utilizing steam have also been proposed. However, even when used motor oil is directly heated, i.e., in the absence of heat transfer surfaces, the nozzles and downstream piping can plug in 24 to 72 hours due to the presence of organo-metallic compounds.
Allowed U.S. patent application Ser. No. 09/026,367, filed Feb. 19, 1998, discloses a process for recovering lube oil base stocks from used lubricating oil formulations containing base oil stock and organo-metallic component by directly contacting used lubricating oil with a heated vapor, e.g., steam, under conditions which at least partially decompose the organo-metallic component and provide a desired volume of pumpable bottoms containing organo-metallic compound decomposition products and an overhead comprising gases and distillable hydrocarbons, with no substantial carryover of metals into the overhead.
It would be advantageous to provide an efficient method for recovering used motor oil by thermal treatment using direct heat exchange in a process which does not require apparatus susceptible to clogging or fouling which can be carried out by continuous addition of used motor oil to the system. It would also be advantageous to provide a process for treating used motor oil which does not require preseparation of light materials or water found in used motor oil as collected.
The present invention is a continuous, plural stage, heated vapor injection process for recovering lube oil base stocks from used lubricating oil containing distillable liquid hydrocarbons and water which comprises providing a continuous flow of used lubricating oil and heated vapor to a first stage and directly contacting said used lubricating oil with said heated vapor and providing a steady state balance of temperature, used lubricating oil addition, and heated vapor addition sufficient to remove substantially all water and optionally some light ends from said first stage as an overhead stream, thereby providing a first stage bottoms fraction containing distillable hydrocarbons; continuously removing said first stage bottoms fraction from said first stage to one or more subsequent stages, and directly contacting said bottoms fraction with said heated vapor under conditions sufficient to provide a subsequent stage bottoms fraction which is 5 to 80 wt. % of the initial volume of said used lubricating oil, and a distillable hydrocarbon overhead; and collecting said distillable hydrocarbon overhead and said bottoms fraction from said subsequent stage(s).
In another aspect, the present invention relates to a plural stage apparatus for treating used lubricating oil comprising: a first stage treating zone comprising an inlet for used motor oil, an inlet for heated vapor, an outlet for vaporized overhead and an outlet for first stage bottoms, a subsequent stage treating zone comprising an inlet for first stage bottoms, an inlet for heated vapor, an outlet for a bottoms fraction, and an outlet for distillable hydrocarbon overhead.
In yet another aspect, the present invention relates to an asphalt blend composition which comprises an asphalt component and a bottoms fraction obtained from used lubricating oil formulations containing distillable liquid hydrocarbons and water comprising: providing a continuous flow of used lubricating oil and heated vapor to a first stage and directly contacting said used lubricating oil with said heated vapor and providing a steady state balance of temperature, used lubricating oil addition, and heated vapor addition sufficient to remove substantially all water, if present and light ends from said first stage as an overhead stream, thereby providing a first stage bottoms fraction containing distillable hydrocarbons; continuously removing said first stage bottoms fraction from said first stage to one or more subsequent stages, and directly contacting said bottoms fraction with said heated vapor under conditions sufficient to provide a subsequent stage bottoms fraction which is 5 to 50 vol. % of the initial volume of said used lubricating oil, and a distillable hydrocarbon overhead; and collecting said bottoms fraction from said subsequent stage(s).
By the term vapor is meant a material in gaseous form as introduced into the present process. This would include those materials which can be in a non-gaseous form at room temperature, e.g., H2O (steam). The heated vapor employed in the present invention is selected from the group of gases/vapors consisting of methane, ethane, propane, and steam. The heated vapor is introduced in the first stage which itself may comprise a vessel at temperatures ranging from 450 to 1800xc2x0 F., preferably from 500 to 1100xc2x0 F., at a rate of 0.1 to 10 pounds/pound of charge, more preferable 0.5 to 5 pounds/pound of charge and most preferably 1 to 3 pounds/pound of charge. Superficial velocities are low enough to prevent entrainment of organo-metallic compounds in the overhead, generally no greater than 5.5 feet per second, preferably no greater than 3 feet per second. Vaporization temperatures achieved in the vessel can range from 400 to 1000xc2x0 F., preferably 550 to 650xc2x0 F. The used lubricating oil is contacted with the heated vapor for a period ranging from 0.1 to 2 hours, e.g., 1 hour, preferably 0.25 to 0.5 hours. The vaporization temperatures, heated vapor (steam) rates, superficial velocities, used lubricating oil addition rates, and contact times are adjusted to provide a preset volume reduction of the total amount of used lubricating oil added to the process (or degree of lift of overhead vapors), e.g., ranging from 20 to 95 wt. %, preferably from 60 to 90 wt. % of the total amount of used lubricating oil added to the vessel.
In one embodiment of the present invention, the heated vapor from the first and/or subsequent stages is recovered from the overhead and recycled to the first stage. This is especially useful where the heated vapor is selected from the group consisting of methane, ethane, and propane.
The above conditions may be varied to adjust the extent of decomposition of the organo-metallic component made up of organo-metallic compounds in the used lubricating oil. Used lubricating oils processed by the present invention may contain organo-metallic compounds in a concentration of 0.01 to 5.0 wt. %. The treatment of the present invention can be used to decompose the organo-metallic component to the extent desired, e.g., sufficient to provide a product having an organo-metallic component concentration of 0.005 wt. % or less, preferably less than 0.001 wt. %.
In an especially preferred embodiment, the heated vapor employed is superheated steam. The fouling of used motor oil-contacted surfaces ordinarily observed during UMO processing does not occur in this embodiment. The use of steam may lower partial pressure of the vaporization of the overhead so that vaporization temperatures no greater than 650xc2x0 F. or even 600xc2x0 F. can be used. Such lower vaporization temperatures combined with lower contact times may be particularly desirable inasmuch as they may minimize the decomposition of valuable additives of the used lubricating oils, such as viscosity index improvers, pour point depressants, defoamants, and detergent-dispersants, which can be present in used lubricating oils in amounts of at least 0.1 wt. %, e.g., ranging from 0.1 to 25 wt. %, preferably 1 to 10 wt. %.
The presence of these high molecular weight polymer additives in the pumpable bottoms fraction can be especially advantageous when the bottoms are added to such products as performance graded asphalts. Alternatively, the pumpable bottoms can be combined with fuel oil; however, the additives thus introduced confer less benefit than in asphalt.
In another preferred embodiment of the invention, the used lubricating oils contain at least 0.1 wt. %, preferably at least 1 wt. % of viscosity index improver, and said vaporization temperatures and contact times are such as to minimize decomposition of said viscosity index improver so as to provide a bottoms fraction containing at least 0.1 wt. %, preferably at least 1 wt. %, viscosity index improver.
In another aspect, the invention relates to a novel asphalt blend composition containing, an asphalt component and the used motor oil bottoms product prepared by the process of the present invention, with or without modification additives such as polymers, chemical gellants, and antioxidants and to paving compositions containing such modified asphalts. Generally, the asphalt blend compositions comprise (a) about 0.1 to about 20 wt. %, preferably about 0.5 wt. % to about 15 wt. % of used motor oil bottoms prepared by the process of the present invention, (b) about 0 to about 20 wt. %, preferably about 0 to about 10 wt. % of a polymer modifier, (c) about 0 to about 7 wt. %, preferably about 0 to about 5 wt. % of a chemical gellant and (d) at least about 80 wt. %, e.g., about 80 wt. % to about 99 wt. %, say, 90 wt. %, of an asphalt component obtained from conventional vacuum distillation, atmospheric distillation, solvent refining, e.g., solvent deasphalting bottoms, or naturally occurring mineral sources, e.g., Trinidad Lake asphalt. All percents herein are by weight of total composition. Asphalt paving compositions of such blend can exhibit a distinct improvement in low temperature properties, in their resistance to thermal cracking and fatigue as defined by the use of the new Superpave Performance Graded (PG) Asphalt Binder Specifications: AASHTO MP1.
In yet another aspect, the present invention relates to a pavement composition comprising aggregate and from about 1-10 wt. % of an asphalt blend containing at least about 80 wt. % of asphalt and from about 0.5-15 wt. % of the bottoms fraction of prepared by the process of the present invention.